Chemical sensors are routinely used to detect the presence and measure the concentration of various chemicals. Example structures and processes related to gas detectors are disclosed in U.S. Pat. No. 6,393,894 and U.S. Pat. No. 4,944,035, which are hereby incorporated by reference. However, many chemical sensors experience baseline drift over the course of their operation.
This drift manifests itself by causing a sensor to report a chemical concentration that is an inaccurate measure of the true chemical concentration. For example, if a sensor's baseline response drifts to a value one unit higher than typical, the sensor will report a chemical concentration of one even if the true chemical concentration is zero. Baseline drift requires the sensor to either be re-calibrated frequently using a reference gas source in order to establish a proper baseline or the use of a poorer sensitivity that accounts for the expected drift. These caveats severely limit the applications for the sensor to those in which signals are well above the baseline drifts between calibrations.